The present disclosure relates to a detecting device, a detecting system, a power transmitting device, a noncontact power transmission system, and a detecting method for detecting the presence of a conductor such as a metal or the like.
Noncontact power transmission systems in which power is supplied on a noncontact basis (wireless feeding) have recently been actively developed. Systems for realizing wireless feeding are broadly classified into two kinds of methods.
One is an electromagnetic induction system already known widely. In the electromagnetic induction system, a degree of coupling between a power transmitting side and a power receiving side is very high, and thus feeding can be performed with high efficiency. However, a coupling coefficient between the power transmitting side and the power receiving side needs to be kept high. Thus, when a distance between the power transmitting side and the power receiving side is increased or there is a positional displacement between the power transmitting side and the power receiving side, efficiency of power transmission between coils on the power transmitting side and the power receiving side (which efficiency will hereinafter be referred to as efficiency between the coils) is greatly degraded.
The other is a method referred to as a magnetic field resonance system. The magnetic field resonance system has a feature of using a resonance phenomenon actively and thereby requiring only a small magnetic flux shared between a feeding source and a feeding destination. The magnetic field resonance system does not degrade the efficiency between the coils even in a case of a small coupling coefficient when a Q-value (Quality factor) is high. The Q-value is an index indicating relation between the retention and a loss of energy of a circuit having the coil on the power transmitting side or the power receiving side (indicating the strength of resonance of a resonant circuit). That is, the magnetic field resonance system has advantages of eliminating a need for alignment between the coil on the power transmitting side and the coil on the power receiving side and providing a high degree of freedom of positions of and a distance between the power transmitting side and the power receiving side.
One of important elements in a noncontact power transmission system is a measure against heat generated by a metallic foreign matter. Irrespective of whether the noncontact power transmission system is of an electromagnetic induction type or a magnetic field resonance type, when feeding is performed on a noncontact basis, and there is a metal between a power transmitting side and a power receiving side, an eddy current may occur in the metal and cause the metal to generate heat. A large number of methods for detecting a metallic foreign matter have been proposed as measures against the generation of the heat. For example, methods using an optical sensor or a temperature sensor are known. However, a detecting method using a sensor entails high cost in a case of a wide feeding range as in the magnetic field resonance system. In a case of a temperature sensor, for example, an output result of the temperature sensor depends on the thermal conductivity of the surroundings of the temperature sensor, so that design limitations are imposed on apparatuses on the power transmitting side and the power receiving side.
Accordingly, a method has been proposed which observes a change in parameter (current, voltage, or the like) when a metallic foreign matter is inserted between the power transmitting side and the power receiving side, and determines whether a metallic foreign matter is present or not. Such a method does not need to impose design limitations or the like, and reduces cost. For example, Japanese Patent Laid-Open No. 2008-206231 (hereinafter referred to as Patent Document 1) proposes a method for detecting a metallic foreign matter on the basis of a degree of modulation (information on changes in amplitude and phase) in communication between the power transmitting side and the power receiving side, and Japanese Patent Laid-Open No. 2001-275280 (hereinafter refereed to as Patent Document 2) proposes a method for detecting a metallic foreign matter on the basis of an eddy current loss (foreign matter detection based on DC-DC efficiency).